A necessary processing such as a back surface grinding treatment for thinning the wafer as thin as possible is applied to a semiconductor wafer having formed thereon a circuit pattern such as IC. For example, by the back surface grinding treatment, a semiconductor wafer having a thickness of about 0.6 mm is ground to a thickness of from 0.1 to 0.4 mm and is then sent to a subsequent dicing process. In processing a semiconductor wafer, for preventing, for example, the wafer from being injured and also for preventing the circuit pattern-formed surface of the wafer from being stained or injured with grinding trashes, etc., a protective member is previously adhered to the circuit pattern-formed surface of the wafer via an automatic adhering apparatus. After applying necessary processing such as a back surface grinding treatment, etc., the protective member is peeled off, and the semiconductor wafer is sent to a wafer-washing process.
Hitherto, as the protective member, a long separator formed by surface-treating a film of polyester, polypropylene, etc., with a silicone release agent having temporarily adhered thereon protective film pieces each with a definite interval via a pressure-sensitive adhesive layer formed on each protective film piece has been known. However, such a protective member has a problem that when the protective film piece is peeled from the separator, a part of the silicone release agent is transferred and adhered onto the surface of the pressure-sensitive adhesive layer and is then adhered to a semiconductor wafer, staining the circuit pattern-formed surface of the wafer.
To overcome this problem, a protective member using a polyethylene film (JP-A-63-177423) or a stretched polypropylene film (JP-A-6-330005) capable of peeling from a pressure-sensitive adhesive layer without treating with a silicone release agent as the separator is proposed. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
However, use of the polyethylene film has a problem that when a protective film is peeled from the separator via an automatic adhering apparatus, elongation of the separator is large and an incorrect action occurs that a part of the protective film is adhered to a semiconductor wafer by a roller, etc., while adhering to the separator, causing the troubles such as the injury of the wafer, etc. Further, use of the stretched polypropylene film also has a problem that the adhesive force to a pressure-sensitive adhesive layer, in particular, an acrylic pressure-sensitive adhesive layer is large, a protective film is adhered to a semiconductor wafer in the state that the stress caused at peeling a protective film from the separator remains in the protective layer, and the stress is added to the wafer at back-surface grinding, causing a warpage of the wafer after grinding.